Conversion of gem-difluoro compounds to fluoroalkenes and fluoroalkapolyenes

ABSTRACT

GEM DIFLUORO COMPOUNDS ARE CONVERTED TO FLUOROALKENES, FLUOROALKADIENES, OR FLUOROALKATRIENES BY CONTACTING SAID GEM-DIFLUORO COMPOUNDS WITH A CATALYST FORMED BY TREATING A FINELY DIVIDED ALUMINA WITH A LIQUID SOLUTION OF AMMONIUM FLUORIDE, AMMONIUM BIFLUORIDE, OR HYDROGEN FLUORIDE, THEREAFTER DRAINING SAID SOLUTION FROM SAID ALUMINA, REPEATING THE TREATING AND DRAINING STEPS, AND THEREAFTER HEATING THE IMPREGNATED CATALYST TO A TEMPERATURE IN THE RANGE OF 300 TO 1000*F. FOR A PERIOD OF TIME IN THE RANGE OF 2 TO 24 HOURS.

United States Patent US. Cl. 260-6535 5 Claims ABSTRACT OF THEDISCLOSURE Gem difluoro compounds are converted to fluoroalkenes,fluoroalkadienes, or fluoroalkatrienes by contacting said gem-difluorocompounds with a catalyst formed by treating a finely divided aluminawith a liquid solution of ammonium fluoride, ammonium bifluoride, orhydrogen fluoride, thereafter draining said solution from said alumina,repeating the treating and draining steps, and thereafter heating theimpregnated catalyst to a temperature in the range of 300 to 1000 F. fora period of time in the range of 2 to 24 hours.

This is a divisional of copending application Ser. No. 788,000, filedDec. 30, 1968, now US. 3,624,167, which is a division of Ser. No.439,475, filed Mar. 12, 1965, now US. Pat. 3,432,441.

This invention relates to a novel catalyst for the preparation offluoroalkenes and fluoroalkapolyenes. In another of its aspects, itrelates to a process for preparing a catalyst useful for convertingacetylenic hydrocarbons to fluoroalkenes, fiuoroalkadienes andfiuoroalkatrienes. More specifically, the process comprises repeatedlycontacting an alumina catalyst with a solution of a fluorinecontainingcompound. In a still further aspect, the invention relates to a processfor regenerating a spent catalyst useful for the production offluoroalkenes, fluoroalkadienes and fiuoroalkatrienes. In a stillfurther aspect, the invention relates to a process for producingfluoroalkenes, fiuoroalkadienes and fluoroalkatrienes from acetylenichydrocarbons. In another of its aspects, the invention relates to theproduction of flouroalkenes and fluoroalkapolyenes from gem-difluorocompounds by passing the gem-difluoro compounds over afluoride-impregnated alumina catalyst prepared according to theinvention.

Fluoroethylene is a desirable monomer for the preparation of polyvinylfluoride. Fluorided alumina and aluminum fluoride-alumina mixtures areknown for their promotion of the addition of hydrogen fluoride toacetylene in the production of fluoroethylene. However, at the requiredtemperatures for the addition the alumina reacts with hydrogen fluorideuntil an equilibrium fluorine content in the catalyts is obtained. Thereaction is exothermic and induces sintering of the catalyst particles,thereby reducing surface area and reducing catalyst activity. Inaddition, the above catalysts apparently are non-selective, promotingthe addition of a second mole of hydrogen fluoride to produce nearlyequal molar quantities of fluoroethylene and 1,1-difluoroethane. Thus,it has become apparent that the method of incorporating fluorine into analumina, or alumina-containing, catalyst is an important aspect of thepreparation of fluoroethylene. I have found that a suitable catalyst forpreparing fluoroethylene from acetylene can be prepared by repeatedlytreating an alumina or alumina-containing actalyst with a solution of afluorine-containing compound.

It is therefore an object of this invention to produce a catalyst forconversion of acetylenic hydrocarbons to.

fluoroalkenes, fluoroalkadienes and fiuoroalkatrienes.

It is a further object of this invention to provide a process for makinga catalyst suitable for conversion of acetylenic hydrocarbons tofluoroalkenes, fluoroalkadienes and fiuoroalkatrienes.

It is a further object of this invention to provide a process forregenerating a catalyst produced by this invention.

It is a still further object of this invention to provide a process forproducing a fluoroalkene, a fluoroalkadiene or a fluoroalkatriene froman acetylenic hydrocarbon.

It is a still further object of this invention to provide a process forconverting gem-difluoro compounds to fluoroalkenes andfiuoroalkapolyenes.

Other aspects, objects and the several advantages of this invention areapparent to one skilled in the art from a study of this disclosure andthe appended claims.

In accordance with my invention, an improved catalyst of higher, morestable activity and selectivity for the production of fiuoroalkenes andfluoroalkapolyenes by the vapor-phase hydrofluorination of acetylenichydrocarbons is obtained by repeated impregnation of etaor gammaaluminaor bauxite with a liquid solution of ammonium fluoride, ammoniumbifiuoride, or hydrogen fluoride. Water is the solvent of choice forpreparing each of these solutions. However, other solvents capable ofmaintaining a sufficient concentration of the fluoride in solution canbe used for the ammonium fluoride and ammonium bifluoride. Examples ofsuch solvents are alcohols and hydroxy-substituted amines. The solventis evaporated from the catalyst after each impregnation; and after thefinal impregnation, the catalyst is subjected to a temperature of about300 to 1000 F., preferably about 600 to 1000 F., usually for about 2 to24 hours. The number of impregnations required varies, depending on thepore volume of the catalyst and the concentration of fluoride in thesolution, but will usually be in the range of 3 to 10, preferably 5 to10. The preferred concentration of ammonium fluoride or ammoniumbifluoride in the impregnating solution is 10 to 50 g./ ml. of solution;when aqueous solutions of hydrogen fluoride are used, the preferredconcentration of the acid is 1 to 20 weight percent. Preferably, theimpregnations are repeated a sufiicient number of times to give acatalyst which, after the final heat treatment at about 300 to 1000 F.,contains 30 to 60 weight percent fluorine. Although the impregnationsare conveniently carried out at room temperature, any temperature atwhich the fluoride remains in liquid solution can be used. In someinstances it is desirable to complete the fluoridation of a partiallyfluorided catalyst by treatment with gaseous hydrogen fluoride, in thepresence or absence of an inert diluent such as nitrogen, helium, argon,or the like, prior to use of the catalyst in the production offluoroalkenes or fluoroalkapolyenes. This vapor-phase fluoridation canbe carried out at a temperature of about 300 to 1000 F., preferablyabout 600 to 800 F.

Further, according to the invention, gem-difluoro compounds, unavoidablyproduced during the production of fluoroalkenes and fluoroalkapolyenes,can be converted to fluoroalkenes and fluoroalkapolyenes by passing thedifluoro compounds over the catalyst of the invention.

The acetylenic hydrocarbons which are preferred for use in thehydrofluorination reaction which employs the catalyst of the inventionhave the formula R.CECR, where R is selected from the group consistingof hydrogen and alkyl and alkenyl radicals containing not more than 8carbon atoms, the total number of carbon atoms in the acetylenichydrocarbons not exceeding 10. Some examples of these preferredacetylenic hydrocarbons are acetylene, propyne, I-butyne, Z-butyne,Z-pentyne, l-hexyne, 3-octyne, Z-decyne, 3-methyl-1-pentyne,2,5-dimethyl-3-hexyne, 1-penten-4-yne, l-hexen-S-yne, 2-hepten-5- yne,3-ethyl-l-octen-6-yne, and 1,8-nonadien-4-yne. The acetylenichydrocarbons containing no unsaturation other than the carbon-to-carbontriple bond are more preferred than those containing alkenyl groups,which tend to make 5 the hydrocarbon more susceptible to undersired sidereactions. Although it is preferable to use acetylenic hydrocarbonscontaining not more than carbon atoms, this preference is not a criticallimitation. In the hydrofluorination of these acetylenic hydrocarbonscontaining not more than 10 carbon atoms, this preference is not acritical limitation. In the hydrofluorination of these acetylenichydrocarbons, the elements of hydrogen fluoride add to the triply bondedcarbon atoms in accordance with the Markownikoff rule to give afiuoroalkene or fluoroalkapolyene. The fluorine atom is attached to oneof the carbon atoms adjacent the newly formed double bond. Gem-difluorocompounds are produced as minor products through the addition of theelements of two molecules of hydrogen fluoride to the triply bondedcarbon atoms.

The mole ratio of hydrogen fluoride to acetylenic hydrocarbon should bein the range of 0.2:1 to 20:1, preferably 1:1 to 2:1. Lower ratiosresult in lower conversion of the acetylenic hydrocarbons, and higherratios give larger amounts of the gem-difluoro compound. The flow rateof the reaction mixture should be 50-5000, preferably 200-1000 volumes(standard conditions) per volume of catalyst per hour. The temperaturein the reaction zone should be SOD-750 F., preferably 600-700 F.Although the pressure is conveniently maintained at substantiallyatmospheric, values somewhat above or below this level, such as up toabout 50 p.s.i.g., can be employed when desired.

Further, according to the invention, there is provided a process forregenerating a spent catalyst used in the process of this invention.After continued use of the catalyst it becomes coated with carbonaceousmaterial and it loses its effectiveness. The catalyst can be regeneratedby passing air in the range of 700-950 F., preferably at about 800 F.through the catalyst bed at a volume low enough to prevent the hot zonetemperature of the bed from rising above 950 F. A chamber is thenflushed with nitrogen and the catalyst temperature is lowered to atemperature in the range of 600-675 F. Hydrogen fluoride vapor is thenpassed over the catalyst at a temperature of approximately 600-675 F. toreplace the lost fluorine.

Impregnation: Volume absorbed, ml.

After the final impregnation and drying the catalyst was heated to 1000F. in a muffle furnace and maintained at this temperature for six hours.The resulting catalyst, which contained 36.2 percent fluorine, was thencompared with two related catalysts for utility in the production offluoroethylene from acetylene and hydrogen fluoride by the processdescribed below.

A vertical l-in. x 32-in. monel tube with a concentrically mountedthermowell -in. o.d.) was packed with about 17 in. of a catalyst, about7 in. of supporting material being present below the catalyst. The spaceabove the catalyst served as a preheat zone. The desired reactortemperature was maintained by the use of a furnace equipped with threeelectric heaters which were electronically controlled. Hydrogen fluoridewas charged to the system in vapor form through a Kel F flow meter, froma vessel maintained at 38 C. by use of a temperaturecontrolled oil bath.Acetylene was charged from a cylinder through a second flow meter.Initially the system was flushed out with dry nitrogen, after whichhydrogen fluoride, in the absence of acetylene, was passed over thecatalyst. Nitrogen was employed as a diluent in the hydrogen fluorideduring the vapor phase fluoridation of catalyst 3. When the desiredconstant temperature and hydrogen fluoride flow rate were obtained, theflow of acetylene was begun. The two reactants were not mixed until theyreached the preheat zone in the top part of the reactor. The reactorefliuent, consisting of hydrogen fluoride, acetylene, fluoroethylene,and 1,1-difluoroethane, was passed through a water-cooled condenser. Theefiluent was then passed through two scrubbing towers containing sodiumhydroxide to remove unreacted hydrogen fluoride; moisture was thenremoved with Drierite. The dry gas free of hydrogen fluoride wascollected and measured in a product trap cooled to -80 C., or passeddirectly to a meter for measurement. Sampling valves were convenientlylocated for gas chromatographic analysis of the dry, hydrogenfluoride-free gas.

As the performance of these catalysts is known to remain essentiallycontant during the first 12 hours of use, each of the hydrofluorinationexperiments was carried out over a 3- to 6-hours period falling withinthe first 12 hours of catalyst use. The conversion of acetylene and themole ratio of fluoroethylene to 1,1-difluoroethane in the product arebased on average values obtained in gas chromatographic analyses madehourly during the 3- to 6-hour experiments.

The results obtained in the hydrofluorination experiments employing eachof three different catalysts are summarized in Table l. The data inTable 1 show that catalyst 1, prepared by the multiple impregnationtechnique of this invention, was more selective in elfecting theproduction of fluoroethylene instead of 1,1-difluoroethane, at the sametime exhibiting a high degree of activity as shown by the highconversion of acetylene. In addition, the activity and selectivity ofcatalyst I remained more stable than did that of the other twocatalysts. Table 1 also shows that the use of catalyst 1 which hadreceived 6 impregnations with aqueous ammonium bifluoride, theconversion of acetylene was only slightly less and the ratio offluoroethylene to 1,1-difluoroethane was much greater than with the useof catalyst 3, which had received no impregnations.

TAB LE 1 CH =CHF Reaction Flow 02H: ClEIsCHF temp, rate, HF/CzHg eonv.,mole ratio Catalyst v./v./hr. mole ratio percent in product Catalyst 1was prepared by the multi is im re nation thod i invention, as describedab p p g me 0 this ove. prepared by breaking %-in. All; commercial pillsb Catalyst 2 was (Harshaw Chemical Co.) to a size of 10-20 mesh; thesepills contained 58.3 percent fluorine by weight.

v Catalyst 3 was prepared by vapor phase fluoridation of eta-aluminawith hydrogen fluoride diluted with nitro en; the resultin eatal st 0tained 55.0 percent fluorine by weight. g g y c n EXAMPIZE 11 Aftercatalyst 1 had been'used for 50 hours in the hydrofluorination ofacetylene, it was reactivated by passing dry air through the'reactor'containing the catalyst at an initial temperature of 800 F. The flowrate of the air was controlled at about 150 volumes per volume ofcatalyst per hour so as to prevent the'temperature of the hot zone whichmoved through the catalyst bed from exceeding 950 F., therebyavoidingsintering of thecatalyst. Determination of the carbon oxides producedduring the combustion showed the carbon content of the catalyst prior toreactivation to have been 10.0 weight percent. Fluorine loss during thecombustion was 2.5 weight percent of the fluorine initially present;this loss was determined by absorption of the evolved hydrogen fluoridein water, and subsequent titration with standard base. After thecombustion was completed, the catalyst chamber was flushed withnitrogen, and the catalyst temperature was lowered to 600-675 F.Hydrogen fluoride vapor was then passed over the catalyst at 600-675 F.for about 1 hour to replace the fluorine lost during the combustion.

To demonstrate the effectiveness of the reactivated catalyst, resultsobtained in the hydrofluorination of acetylene during 6-hour experimentsimmediately preceding and immediately following the reactivation werecompared. In each of these experiments hydrogen fluoride and acetylenein an HF/C H mole ratio of 1.4 were passed, at atmospheric pressure andat a total flow rate of 400 volumes per volume of catalyst per hour,over the catalyst maintained at a temperature of 675 F. The table belowshows the acetylene conversion, mole ratio of fluoroethylene to1,1-difluoroethane in the product, and per pass yield of fluoroethyleneobtained in each of the 6-hour experiments. From the table it can beseen that reactivation rendered the catalyst decidedly improved withrespect to acetylene conversion and fluoroethylene yield. Although thereactivated catalyst gave a lower ratio of fluoroethylene to1,1-difluoroethane, other experiments have shown that this ratioincreases with continued use of the catalyst following reactivation.

TABLE 2 Before catalyst reactivation:

C H conv. percent 43 CH =CHF/CH CHF mole ratio in product 8.5 Per passyield, g. CH =CHF per g. C H

Per pass yield, g. CH =CHF per g. C H

charged 1.3

It is to he understood that although the invention is described for themost part with regard to the production of fluoroalkenes, it is obviousthat fluoroalkapolyenes can also be produced by the invention. Thus, theinvention is not necessarily to be limited to the production offiuoroalkenes but it can also include the production offluoroalkadienes, fluoroalkatrienes, and the like. Examples of suchfluoroalkenes and fluoroalkapolyenes produced according to the inventioninclude fluoroethylene, 2-fluoropropene, 2-fluoro-1-butene,Z-fluoro-Z-butene, 2-fluoro-1- hexene, 4-fluoro-3-octene,2-fiuoro-1-decene, 3-methyl-2- fluoro-l-pentene,2,5-dimethyl-3-fluoro-3-hexene, Z-fluoro- 1,4-pentadiene,2-fluoro-1,5-hexadiene, 3-fluoro-2,5-hepadiene,3-ethyl-6-fluoro-1,6-octadiene, and 4-fluoro-1,4,8- nonatriene.

The gem-difluoro compounds, such as gem-difluoroalkanes,gem-difluoroalkenes, and gem-difluoroalkadienes, which are unavoidablyproduced in the production of the fluoroalkenes and fluoroalkapolyenesaccording to the invention, can be converted to the desiredfluoroalkenes and fluoroalkapolyenes by recycling the gem-difluorocompounds over the catalyst of this invention. The gem-difluorocompounds are produced as a minor product through the addition of theelements of two molecules of hydrogen fluoride to the triply bondedcarbon atoms.

The catalyst prepared according to the invention can be used for thedehydrofluorination of gem-difluoro compounds. In such a process, thegem-difluoro compounds can be passed over the fluoride-impregnatedcatalyst at flow rates of 10 to 1000, and preferably 50 to 200, volumes(standard conditions) per volume of catalyst per hour, and a reactiontemperature of 500 F. to 900 F., generally in the range of 675 F. to 725F. The pressure is substantially atmospheric, although higher or lowerpressures can be employed, as desired. The reaction can take place withor without the presence of an acetylenic compound.

The alumina used to prepare the catalyst is of a high porous, highsurface area type. Preferably, the alumina is etaor gamma-alumina; lesspreferably, the alumina may be bauxite. The alumina can be used alonefor the catalyst formation or it can be combined with a metalcontainingconstituent. This constituent is a fluoride of zinc, chromium, cobalt,silver, copper, vanadium, iron,

or nickel, or a salt, oxide, or other form convertible to a fluoride bythe subsequent high temperature reaction with hydrogen fluoride. Themetal-containing constituent can be incorporated in the alumina in anyconvenient manner. For example, the metal compound can be ground withthe alumina and the resulting composite then pelleted. Alternately, thealumina can be impregnated with a solution containing the metal.

The catalyst of the invention can be used to aid in the separation ofacetylenic hydrocarbons from other hydrocarbons of similar boiling pointor molecular weight. As an example, acetylene can be removed fromstreams containing ethylene and/ or ethane; propyne can be separatedfrom propylene and/or propane; and butyne can be separated from butenesand/or butanes. In such a process, the acetylenic hydrocarbons would beconverted to fluoroalkenes which could then be easily separated by aphysical process such as fractionation, from the other unreactedhydrocarbons.

Reasonable variation and modification are possible within the scope ofthe foregoing disclosure and the appended claims to the invention, theessence of which is that a catalyst suitable for producingfluoroalkenes, fluoroalkadienes and fluoroalkatrienes from acetylenichydrocarbons can be prepared by repeated impregnation of at least one ofa gamma-alumina, eta-alumina, or bauxite catalyst with a solution of afluorine-containing compound, followed by heating of said catalyst aftereach impregnation step; and a spent fluorine-containing alumina catalystsuitable for production of fluoroalkenes, fiuoroalkadienes andfluoroalkatrienes can be regenerated by heating said catalyst to atemperature in the range of 700 to 950 F., cooling said catalyst to atemperature in the range of 600 to 675 F., and contacting said catalystwith a hydrogen fluoride gas; and that gem-difluoro compounds areconverted to fluoroalkenes and fluoralkapolyenes by passing thegem-difluoro compounds over a fluoride-containing alumina catalyst.

I claim:

1. A process for converting gem-difiuoro compounds selected from thegroup consisting of gem-difluoralkanes, gem-difluoroalkenes, andgem-difluoroal'kadienes, to fluoroalkenes, fiuoroalkadienes, andfluoroalkatrienes comprising contacting, at a temperature of 500 F. to900 F., said gem-difluoro compounds with a catalyst formed by treating afinely divided alumina catalyst comprising at least one ofgamma-alumina, eta-alumina, and bauxite with a 1-20 weight percentliquid solution of at least one of NH F, NH F-HF, and HF, draining saidsolution from said alumina, repeating said treating and draining steps,and thereafter heating said impregnated catalyst to a temperature in therange of 300 to 1000 F. for a period 7 of time in the range of 2 to 24hours to provide a catalyst containing 30-60 weight percent fluorine.

2. A process according to claim 1 wherein said catalyst is heated to atemperature of about 120 C. after each draining step; and wherein saidimpregnated catalyst is heated to a temperature of about 1000 F. for atime of about 6 hours.

3. A process according to claim 1 wherein said catalyst is contactedafter impregnation with HF vapors at a temperature between 300 and 1000F.

4. A process according to claim 1 wherein said solution is a solution ofammonium bifluoride, said gem-difluoro compounds being passed over saidcatalyst at a flow rate of 10 to 1000 volumes per volume of catalyst perhour.

5. A method according to claim 1 wherein said gemdifluoro compounds aregem-difiuoroalkanes and said gem-difluoro compounds are converted tofluoroalkenes.

References Cited UNITED STATES PATENTS 3,456,025 7/1969 Gardner 260-65352,478,032 8/1949 Miller et a1. 260653.5

DANIEL D. HORWITZ, Primary Examiner US. Cl. X.R.

